The present invention relates to variable displacement axial piston hydraulic devices of the cradle and swash type, and more particularly, to a clocking or timing mechanism for the bearing cage of a roller bearing assembly which supports the swashplate relative to the cradle.
Variable displacement axial piston devices of the type to which the present invention relates are most commonly utilized as pumps, and the invention will be described in connection therewith, although it should be understood that the invention is also applicable to variable displacement motors.
In variable displacement axial piston pumps of the type to which the invention relates, the pump housing defines a concave cradle surface, and the tiltable swashplate defines a mating, convex surface. Disposed between the cradle and the swash there is typically a pair of arcuate roller bearing assemblies, disposed on opposite transverse sides of the input shaft, each of which includes some sort of bearing cage.
As is well known to those skilled in pump art, there is a substantial axial load applied to the roller bearing set when the swash is displaced and the pump is pumping pressurized fluid, perhaps with pressures in the range of 6000 psi.
As is well known to those skilled in the bearing art, the bearing life, in this particular environment, is optimized by insuring that the roller bearings engage in a purely rolling motion with regard to both the concave cradle surface and the convex surface of the swashplate.
In order to achieve the desired rolling motion of tile bearings, the prior art cradle and swash type axial piston pumps have typically utilized what is referred to as a "bearing-clocking" mechanism, the function of which is to prevent slipping or sliding of either of the roller bearing sets, as the swashplate is displaced between its neutral position and its various displaced, operating positions. The typical prior art bearing-clocking mechanism has included a clocking member having one end pivotally connected to the pump housing and an opposite end connected to the swashplate in a manner which permits both sliding and pivotal motion therebetween. Intermediate the two ends, the clocking member is typically in engagement with, or attached to, the cage of the roller bearing assembly in a manner which also permits both sliding and pivotal movement. Examples of prior art bearing-clocking mechanisms may be seen in U.S. Pat. Nos. 4,029,367; 5,024,143; and 5,390,584.
Unfortunately, the prior art bearing-clocking mechanisms have not been totally satisfactory. For example, each of the clocking members in the above-cited patents comprises a member fabricated from wire such that the clocking member is "flexurally elastic", thus permitting some deviation of the roller bearing assembly from its desired, purely rolling relationship with both the cradle and swash.
In addition, the use of a clocking member formed from wire typically requires, in order to obtain a "slide and pivot" connection with the swashplate, that the wire member pass through a relatively close clearance hole drilled diametrally through a cylindrical swivel member, which, in turn is received within a close clearance cylindrical bore drilled in (for example) the end surface of the swashplate. The use of such a swivel member, and the required machining means that the bearing-clocking mechanism is either quite expensive to manufacture, or if manufactured inexpensively, has a substantial amount of inaccuracy associated with it. Such inaccuracy is manifested in sliding contact between the roller bearings and either the cradle or swash which, as was mentioned previously, can lead to reduced bearing life.